There is great interest in photon up-conversion devices in many fields. In particular in the field of devices capable of allowing humans to see images of scenes that are in nearly total darkness. Particularly important in this respect are devices that are capable of converting short wavelength infrared (SWIR) images into visible ones.
The importance of the SWIR range of wavelengths is that the spectral irradiance of natural light sources such as nightglow known also as airglow is several times stronger in the SWIR range than in the near infrared (NIR) range. Also the transparency through fog and dust is much higher in the SWIR range than in the visible or NIR. Thus scenes and objects that cannot be seen in visible light even in daylight can be viewed using SWIR natural light. In addition in this wavelength range the device doesn't need cooling.
In general, present day advanced SWIR to visible up-conversion devices have several deficiencies including high cost, relatively large size and weight, and in some cases require cooling using liquid nitrogen. In addition, other proposed up-conversion devices suffer from low quantum efficiency due to low SWIR photon absorption and Low efficiency of the conversion process.
Liquid crystals spatial light modulators are well established technology [1]. By using spatial light modulators (SLM), the phase and/or amplitude of a beam of light can be modulated. There are two standard types of light modulation using liquid crystals (LC) devices. The first type is the so called electrically addressed SLM (EASLM) wherein an electrical signal drives the orientation of the LC molecules which in turn causes a phase and/or amplitude modulation of the beam transmitted/reflected trough the device. The second type is the so called optically addressed SLM (OASLM), wherein an optical signal with wavelength λ1 drives the LC molecules orientation which in turn causes a phase and/or amplitude modulation of a second beam with wavelength λ2. The driving signal is usually called the writing beam, whereas the transmitted/reflected beam is usually called the reading beam; this writing beam usually absorbed by a photo conductive layer and the liquid crystals act as a modulator [2] on the reading beam.
It is a purpose of the present invention to provide a small low-cost up-conversion device for converting SWIR images into visible images.
Further purposes and advantages of this invention will appear as the description proceeds.